Some hybrid vehicles may include a driveline disconnect clutch that may mechanically isolate one portion of a driveline from a second portion of the driveline. In one hybrid configuration, the driveline disconnect clutch may isolate an engine from an electric motor if the driveline disconnect clutch is in an open state. The driveline disconnect clutch mechanically couples the engine to the motor when the driveline disconnect clutch is in a closed state. The driveline disconnect clutch may also be partially closed so that the electric motor rotates the engine during engine starting. However, it may be difficult to maintain torque applied to vehicle wheels when the driveline disconnect clutch is partially engaged because the driveline disconnect clutch torque may be difficult to estimate. Consequently, a torque reduction to the vehicle wheels may occur during engine starting.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of operating a hybrid vehicle driveline, comprising: automatically stopping an engine and opening a driveline disconnect clutch in response to an engine stop request; and automatically starting the engine in response to an engine start request, automatically starting the engine includes partially closing the driveline disconnect clutch to rotate the engine at a cranking speed and at least partially opening the driveline disconnect clutch in response to an combustion event.
By partially closing a driveline disconnect clutch to crank an engine and at least partially opening the driveline disconnect clutch in response to a combustion event or other engine rotation related event, it may be possible to provide the technical result of maintaining torque applied to vehicle wheels during engine starting. At least partially opening the driveline disconnect clutch after a combustion event may reduce the amount of torque transferred from a driveline integrated starter generator to the engine being started. Further, the amount of time torque is transferred from the driveline integrated starter generator to the engine may be reduced so that the effect of any disconnect clutch torque estimation error may be reduced. Additionally, timing of opening the driveline disconnect clutch is made uniform between engine starts so that the vehicle operates in a similar way between different engine starts.
The present description may provide several advantages. Specifically, the approach may reduce driveline torque disturbances of a hybrid driveline. Further, the approach may improve vehicle drivability. Further still, the approach may reduce driveline wear, thereby increasing the operating life of the driveline.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.